Direct Computations of Boundary Layers Distorted by Migrating Wakes in a Linear Compressor Cascade

A Direct Numerical Simulation (DNS) of flow in the V103 Low-Pressure (LP) compressor cascade with incoming wakes was performed. The computational geometry was chosen largely in accordance with the setup of the experiments performed by Hilgenfeld and Pfitzner (J Turbomach 126:493-500, 2004) at the University of the Armed Forces in Munich. The computations were carried out on the NEC-SX8 in Stuttgart using 64 processors and 85 million grid points. The incoming wakes stemmed from a separate DNS of incompressible flow around a circular cylinder with a Reynolds number of Re (d) = 3300 (based on mean inflow velocity and cylinder diameter). The boundary layer along the suction surface of the blade was found to separate and roll up due to a Kelvin-Helmholtz instability triggered by the periodically passing wakes. Inside the rolls further transition to turbulence was found to occur. The boundary-layer flow along the pressure surface did not separate, instead it underwent by-pass transition.